Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
Photolithography employs photoresist to create a patterned structure that protects the underlying surface from subsequent fabrication steps, such as chemical etching. There are two types of photoresists in common use, positive photoresists and negative photoresists. The positive photoresists are sensitized when exposed to ultraviolet light so that exposed areas will dissolve in a developer solution leaving behind unexposed areas. The negative photoresists are hardened by exposure to ultraviolet light so exposed areas are inhibited from being dissolved by the developer solution while unexposed areas are dissolved.
Although existing photoresist have been generally adequate for their intended purpose, they have not been entirely satisfactory in all aspects.